Commit fe192fe58f made it possible for
events to properly propagate to the top window. As on Windows Enter is
also used for navigation, i.e. used to trigger the dialogs default action,
which in our case seems to be quit.
Tell the wxSpinCtrl to fire wxEVT_TEXT_ENTER instead and handle it.
The wxCommandEvent wxEVT_TEXT_ENTER doesn't carry the value, so need to
use dynamic event binding (which is preferred way anyway).
Also show the numPlayerSpinner as a spinner instead of a text field to
match visuals to actual behaviour.
Fixes: #9026
Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>